====== Microcirculatory changes ======
The techniques used for identification of microcirculatory changes are [[xenon CT]] scanning, [[positron emission tomography]], [[single-photon emission computed tomography]], [[MRI perfusion]] imaging, and [[CT perfusion]] ([[CTP]]) with CTP being in advantage because of its low cost, rapid imaging, high spatial resolution, and ease of performance
((Zhang H, Zhang B, Li S, Liang C, Xu K, Li S. Whole brain CT
perfusion combined with CT angiography in patients with sub-
arachnoid haemorrhage and cerebral vasospasm. Clin Neurol
Neurosurg. 2013;115:2496–501.))

Apart from imaging techniques, the clinical symptoms and the neurological examination of the patient play a cru-
cial role. The disadvantage is that by the time [[cerebral vasospasm]] cause clinical symptoms, the ischemic event may have progressed too far, and the chance of a therapeutic intervention may have been missed.